抄録
Problem: Although we know very little about the physiology of cortica activity, it may be assumed with high degree of probability that the excitatory process initiated in a definite point of the cortex by stimulation of the receptor apparatus irradiates into the surrounding region, deminishing in intensity as the distance increases from the original excitatory focus. One of the best evidences to support this hypothesis was presented by the suggestive research of Bernstein. It was pointed out by him that in the case of cutaneous perception there is a spread of ex citation by stimulation with a single point; thus, two stimulus points close together give rise to an impression of a single touch. I think we may say that all psychologists can hardly doubt the validity of this theory in its general implication. My own treatment of the subject in this paper follows a line which is similar in some respects to that of Bernstein's theory. However, the similarity is dictated not by adherence to the truth of his explanation itself but rather by a common basis of thought in brain physiology. In short, it is one of the ultimate objects of my investigation to infer the cortical interaction in response to visual stimulation by using the amount of the illusion as an index of irradiation.
Experiments: In the preceding papers the writer has reported a series of experiments on the illusion of contrast and confluence and on the illusion of filled space. In the present paper the preceding analysis will be extended to cover other new illusion figures which are assumed to play an important part in our investigation.
Now, the limiting case of the illusion of filled space may be reached by gradually altering the length of the interpolated inner line of the ordinary illusion diagram (Fig. 1. A, A, A.). The outside distances of the diagram A, A, A, although actually equal, appear to be of unequal length, owing to the different infiuences of the interpolated inner stimuli. Using these diagrams, an attempt was made to obtain quantitative data on the effect of the inner longer line upon the outer picture.
We shall begin with an experiment in which the space interval between the outer two lines was varied, the size of the inner line being kept constant (Fig. 1. C, C, C). The general course of the change of the illusion is shown in Fig. 2. The ordinate indicates the amount of the illusion, the abscissa the outer distance. From the curve we see quite clearly that the space tends to be underestimated (contrast) when the outer lines are closely adjacent to the inner one. This facts seems to show that the amount of the illusion depends on the strength of the interpolated stimulus. If strong, it has a contrast effect (underestimation), if weak, an assimilative one (overestimation).
Fig. 1.
Fig. 2.
There is another experiment that seems to support the present result. In the above experiment a measurment was made with the diagram in which the distance between the outer lines was variable, while the size of the inner line Was kept constant. In the following experiment I have sought, on the contrary, to determine a relation between the size of the inner line and the amount of the illusion, the size of the outer picture being kept constant (Fig. 1. A, A, A). The experimental result is shown in Fig. 3. It follows from the curve that the amount of the illusion varies quite regularly with the change in the length of the inner line. The overestimation (assimilation) decreases with the increase in size of the inner line, and the illusion is reversed when the inner line is sufficiently long; so that there is a critical point (an indifferent point) between the two, where no effect results.
